A solid electrolytic capacitor is used for canceling a noise generated from an electronic device such as a CPU, for example. Operation speed of CPUs has been improved to a large degree. With respect to a solid electrolytic capacitor, therefore, excellent noise cancellation performance for a wide frequency band including a high frequency band is demanded. A solid electrolytic capacitor is used also for assisting a power supply system for supplying power to an electronic device. In accordance with an increase in clock speed and digitalization of electronic devices, a solid electrolytic capacitor is demanded which is capable of realizing high power supply at high speed. To realize the high power supply, it is necessary that the capacitance is large and that the heat generation at the porous body is reduced.
The frequency characteristics of the impedance Z of a solid electrolytic capacitor is determined by the following formula 1.Z=√{square root over ((R2+(1/ωC−ωL)2))}  [Formula 1]
In the formula 1, ω represents angular velocity, which corresponds to 2π times the frequency. Further, C, R, and L represent the capacitance, the resistance, and the inductance of the solid electrolytic capacitor, respectively. As will be understood from the above formula, in a frequency band lower than the self-resonant frequency, 1/ωC is the major determinant of the impedance Z. Therefore, the impedance can be decreased by increasing the capacitance C. In a high frequency band near the self-resonant frequency, the resistance R is the major determinant. Therefore, to decrease the impedance, the ESR (equivalent series resistance) needs to be decreased. Further, in an ultra high frequency range higher than the self-resonant frequency, ωL is the major determinant. Therefore, to decrease the impedance, the ESL (equivalent series inductance) needs to be decreased. The larger the volume of a porous sintered body is, the higher the ESL of the solid electrolytic capacitor is. Therefore, as the capacitance is increased, decreasing of the impedance in an ultra high frequency range becomes more difficult.
For instance, a solid electrolytic capacitor includes a porous sintered body of a valve metal such as tantalum or niobium and a plurality of anode terminals projecting out from the porous sintered body. (See Patent Document 1, for example) FIGS. 23 and 24 illustrate an example of such a solid electrolytic capacitor. The solid electrolytic capacitor B includes three anode wires 92 projecting from a porous sintered body 91, and the projecting portions serve as anode terminals 93. As shown in FIG. 24, the anode terminals 93 are electrically connected to each other via an anode conduction member 94. A cathode conduction member 95 is electrically connected to a solid electrolytic layer (not shown) formed on a surface of the porous sintered body 91 via a conductive resin layer 96 made of silver paste, for example. The conduction members 94, 95 are electrically connected to an external anode terminal and an external cathode terminal (not shown) for external connection, respectively. The solid electrolytic capacitor B is structured as a so-called two-terminal solid electrolytic capacitor. In the solid electrolytic capacitor B, the ESR is decreased by the provision of the three anode terminals 93.
However, as shown in FIG. 23, the three anode wires 92 extend into the porous sintered body 91 through the same surface of the sintered body in the same direction. In this figure, the maximum of the distances between portions of the conductive resin layer 96 and the anode wires 92 is indicated as the maximum distance b. In the solid electrolytic capacitor B, the maximum distance b is the distance between an anode wire 92 and the portion of the conductive resin layer 96 located at an end of the surface which is opposite from the surface through which the anode wires 92 extend. The larger the maximum distance B is, the higher the resistance and inductance between the anode terminals 93 and the conductive resin layer 96 is. Particularly, when the size of the porous sintered body 91 is increased to increase the capacitance or the porous sintered body 91 is made flat to decrease the ESL, the maximum distance b increases. In such a case, the ESR and the ESL cannot be decreased, so that the high frequency characteristics cannot be sufficiently enhanced. Moreover, when the size of the porous sintered body is increased to realize high power supply, the heat generation at the porous sintered body 91 is increased. Therefore, the heat dissipation performance needs to be enhanced.
Patent Document 1: JP-A-2001-57319 (FIGS. 2 and 3)